So I have a 1992 300E 2.6L and I had a mechanic leave the serpentine belt off my car in my drive way and he never came back. The fan is still on, he removed the fan guard and shroud. I tried to put the belt back on but it seems impossible even following the diagram order. Can the belt be put back on with the fan still on or do I have to remove the fan? Also the benz started having all the lights on the dash turn on when i turned the sterring wheel, i was told it had something to do with the drive belt, or belt tensioner so I called a mechanic over and he said the water pump was going bad and that was causing the car to not generate the energy needed to drive it because the water pump pully didnt turn easily. Does that sound correct?

Firstly, the belt can be put on with the fan in place. You need to loosen the belt tensioner to be able to put the belt in. Not sure what type of tensioner your car has but you should be able to find out online. Not sure about your lights, but the water pump should be able to spin freely by hand. If not, that is a problem.

https://youtu.be/JUzOS2EKxbY

We recommend removal of the fan for more access and ease of the job.

Also, the lights are likely coming on your dash because the drive belt isn't on so there's nothing turning the alternator, water pump, etc.

-Matt